{"id":1947,"date":"2014-02-05T17:32:48","date_gmt":"2014-02-05T17:32:48","guid":{"rendered":"https:\/\/www.anagram.at\/en\/diplomarbeit\/camera-model-with-lens\/"},"modified":"2014-02-05T17:32:48","modified_gmt":"2014-02-05T17:32:48","slug":"camera-model-with-lens","status":"publish","type":"page","link":"https:\/\/www.anagram.at\/en\/diplomarbeit\/camera-model-with-lens\/","title":{"rendered":"Camera Model with Lens"},"content":{"rendered":"


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\n Next:<\/b> Camera Calibration<\/a>
\n Up:<\/b> Perspective Projection<\/a>
\n Previous:<\/b> The Pinhole Camera<\/a>
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\nCamera Model with Lens<\/a>
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\nThe pinhole camera has the problem that the pinhole should be almost infinitely small, but the smaller the pinhole, the fewer light enters the camera and the longer exposure time is needed. In a dynamic environment this is not possible because the objects in the scene are moving. As a result the pinhole camera is not used in real photography. In reality lenses are used to project the light onto the sensor chip. Figure 2.3<\/a> shows how the light-rays reflected by an object are projected through a lens. \"$ is an object in the real world,
\n\"$ is the distance between \"$ and the lens. \"$ is the focal distance of the lens, \"$ is the effective focal length (distance between the lens and the projected object \"$) and \"$ is the projected object. Light is reflected at the object \"$ and some of the light-rays enter the lens where they are refracted towards the sensor plane and form the object \"$. The relation between these parameters can be written in a mathematical form.\n<\/p>\n\n

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\"$displaystyle<\/td>\n\n(2.10)<\/td>\n<\/tr>\n<\/table>\n<\/div>\n


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<\/p>\n\n\n
Figure 2.3:<\/strong>
\nLens Geometry<\/caption>\n
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\n <\/div>\n<\/td>\n<\/tr>\n<\/table>\n<\/div>\n

As a result of Equation 2.10<\/a>, the focal length<\/i> of the lens and the effective focal length<\/i> are only the same if an object infinitely far away is focused. For reconstruction,
\n\"$ has to be approximated, thus the effective focal length<\/i> has to be computed. As one can see in Equation 2.10<\/a>, \"$ strongly depends on the focused objects and should be chosen so that the objects of interest are focused. Objects that are closer or further away will not be mapped as points but as circles. This happens because the correct image point lies behind or in front of the image plane. Areas which are not focused thus look blurred. There are some general laws which can help choosing the correct lens for a given problem.<\/p>\n